11.26am: Good morning. There is uncertainty today over what precisely happened in the small Syrian town of Tremseh on Thursday night.

While reports from locals and opposition activists indicate that more than 150 died during a brutal massacre by regime thugs, or shabiha, UN observers on the ground have now said evidence they have seen points towards a clash between the heavily-armed army of Bashar al-Assad and local opposition fighters.

There is also apparent uncertainty over the death toll.

Claims and counter-claims, rumour and speculation abound. We'll be updating this blog throughout the day as more information emerges.

11.36am: The Guardian's Martin Chulov has written a wrap-up of the situation as it currently stands here.

The main points are as follows:

• Late last night, the UN monitoring mission released a statement saying that the military attack on Tremseh appeared to have mainly targeted guerilla forces and their supporters. It said:

The attack on Tremseh appeared targeted at specific groups and houses, mainly of army defectors and activists.

• Of 103 fatalities recorded by opposition sources, all are male. Chulov says this is "a fact that adds weight to the view that fighting-aged males were at least partly targeted during the assault."

• However Chulov has himself spoken to local residents who insist they were all targets of a bombardment which involved mortars, artillery and helicopters. They claim that close to 150 people from the town are either dead or missing.

In his report for the Observer today, Chulov quotes one resident of Tremseh as saying:

The bombardment started at 5.30am and ended at 2pm. The incursion started at midday from the north of the village. Shabiha and regime military men entered the village and occupied the roofs of high buildings and shot at anything moving.

They shot many civilians in the head and then burned the bodies. They handcuffed civilians and then shot them in the head. They burned shops and houses with families inside. After what happened, the FSA [Free Syrian Army] members tried to get inside the village to help with burying the martyrs and tending to the wounded but they couldn't.

The criminals took many martyrs' bodies and wounded civilians with them and there are many missing people and burnt dead bodies with no way to identify them.

11.50am: What actually happened in Tremseh remains "murky", the New York Times says, adding that evidence available suggests events "more closely followed the Syrian government account" than that of opposition activists.

The Syrian government has today dismissed the reports of a massacre, rejecting special envoy Kofi Annan's claims that heavy weapons and helicopters were used in clashes. AP reports:

Jihad Makdissi, a spokesman for the Foreign Ministry, said security forces killed 37 fighters and two civilians in a campaign against the town, from which the government said rebels were launching attacks on other areas.

"Government forces did not use planes, or helicopters, or tanks or artillery. The heaviest weapon used was an RPG (rocket propelled grenade)," Makdissi t o ld reporters at a news conference in Damascus.

"Yesterday we received a letter from Mr. Kofi Annan addressed to the Foreign Minister Walid al-Moualem. The least that can be said about this letter about what happened in Tremseh is that it did not rely on facts. As diplomatically as possible, we say that this letter was very rushed."

Justifying its belief that the government's version of events looks likely to be the more truthful, the New York Times details the new claims of the UN, as well as uncertainty over the death toll. It concludes:

In previous massacres, however, like the one in Houla in late May, there was the immediate synchronization between the long lists of civilian names, the gruesome videos of dead women and children, and corroboration by United Nations observers who faulted the Syrian Army for using tank shells and other heavy weaponry against a civilian area. That is missing in the case of Tremseh.

12.06pm: UN observers are expected to return to Tremseh today, AP reports, bringing hope they may be able to shed new light on the events of Thursday night.

The wire's latest dispatch has this take on the UN's statement last night.

Some of the emerging details suggested that, rather than the outright shelling of civilians that the opposition has depicted, the violence in Tremseh may have been a lopsided fight between the army pursuing the opposition and activists and locals trying to defend the village.

Nearly all of the dead are men, including dozens of armed rebels. The U.N. observers said the assault appeared to target specific homes of army defectors or opposition figures.

Running tolls ranged from around 100 to 152, including dozens of bodies buried in neighboring villages or burned beyond recognition. The activists expected the number to rise since hundreds of residents remain unaccounted for, and locals believe bodies remained in nearby fields or were dumped into the Orontes River.

12.12pm: Dutch journalist Sander van Hoorn, who visited Tremseh yesterday, has this to say about the Syrian government's explanation this morning.

Jist of my tweets by @OguzArikboga:"difficult to confirm oppos.'s version of what happened,but gov.'s version can be ruled out" #Syria

Earlier, van Hoorn tweeted that, while he had reason to believe there had been shelling and many deaths, he could not support the idea there had been a massacre like the one that took place in Houla earlier this year.

>>So: Yes, there was fighting here. #Tremseh got shelled and a lot of people died. But I did not see clear signs of a massacre #Syria >>

12.31pm: The International Committee of the Red Cross says it now considers the conflict in Syria a civil war, meaning international humanitarian law applies throughout the country, reports AP.

The Geneva-based group's assessment is an important reference that helps parties in a conflict determine how much and what type of force they can or cannot use.

ICRC spokesman Hicham Hassan said Sunday that the humanitarian law now applies wherever hostilities are taking place in Syria, where fighting has spread beyond the hotspots of Idlib, Homs and Hama.

International humanitarian law grants parties to a conflict the right to use appropriate force to achieve their aims. But attacks on civilians and abuse or killing of detainees can constitute war crimes.

1.10pm: An update from AP on the Red Cross's change in stance on Syria.

"We are now talking about a non-international armed conflict in the country," ICRC spokesman Hicham Hassan said.

Previously, the ICRC had restricted its assessment of the scope of the conflict to the hotspots of Idlib, Homs and Hama, but Hassan said the organization had determined the violence has spread beyond those areas.

"Hostilities have spread to other areas of the country," Hassan told The Associated Press. "International humanitarian law applies to all areas where hostilities are taking place."

1.28pm: A Spanish photojournalist who visited Tremseh on Saturday said he was in no doubt the troops had used heavy weaponry in an attack on the town.

Daniel Leal Olivas, who had been in Syria for three weeks, told Al Jazeera he had seen tank tracks, mortar shells and dozens of burned houses in Tremseh. Residents had told him the shabiha had used "all the power they had" to attack the town.

As we got there, we found obvious proof of heavy weapons. All the tank tracks were in the ground, very fresh. Everyone was in the town very nervous, trying to show us what happened in the town. There was heavy marks of shelling- not only tanks, mortars too. We saw there...were heavy weapons used in that town against the civil population.

Asked if the weaponry could not have been used- as the government claims- by opposition fighters, Leal Olivas said he thought that was very unlikely. From what he had seen of the rebels during his time in Syria, he said, none of them "have the amount of weapons we saw in Tremseh."

We saw all the tracks and everyone was holding the shells of the tanks, and you can see in the walls in the ministry of the town, [it was] very easy to identify there were tanks there. Everyone was [saying] 'tanks came here; not only tanks, many soldiers came here'. [It was] very obvious to see.

2.17pm: The violence in Syria shows no sign of ebbing.

The LCC network of opposition activists has posted a report on their Facebook site saying that a village near Tremseh is currently being besieged by tanks "from four directions". It adds: "Fears of a new massacre similar to Treimseh massacre."

Meanwhile, in Damascus, several people were wounded earlier today when an explosion hit a bus carrying security forces. Reuters reports:

Residents said they heard a powerful blast, followed by the sirens of ambulances rushing toward Damascus's southern ring road near the neighbourhood of Midan.

Some activists said more than one member of the security forces was killed in the attack, but others said there were no dead, only wounded. They said the blast appeared to have been caused by an improvised explosive device that had been stuck onto the bus.

2.48pm: Syrian state TV has broadcast claims that, amid the wreckage of Tremseh, a Turkish identification card belonging to a known fighter had been found.

State television also broadcast pictures of a roomful of weapons that it said had been captured from the town, the inventory mostly underscoring just what a crude and simple arsenal the opposition uses. It included 54 guns, 9 rocket-propelled grenade launchers, 5,000 cartridges, 25 satellite telephones and 24 mortars, the latter looking as if they had been welded by hand.

The broadcast also showed the identification card of what it said was a Turkish fighter in the group, and a captured man named Abdelsalem Darwish said there had been a Turkish fighter and some Libyans there, as well as money and arms from Turkey.

This claim, however, is disputed. BrownMoses, prolific commenter below the line on this blog whose own blog is here, writes that the card "has a few features that suggest the individual isn't Turkish".

First the name isn't a typically Turkish name, and Hama is mentioned on the card, which would make sense as the name at the top, Islahiye, is the location of a major Syrian refugee camp. It also happens to look nothing like a Turkish ID card.

These vicious massacres, these attempts at genocide, these inhuman savageries are nothing but the footsteps of a regime that is on its way out. Sooner or later, these tyrants with blood on their hands will go and the people of Syria will in the end make them pay.

4.01pm: The south of the Syrian capital, Damascus, has today seen some of its heaviest daytime fighting yet, Reuters reports.

Activist Samir al-Shami, who spoke to Reuters by Skype from Damascus, said the fighting was under way in the poor al-Tadamon district, after a night of sustained battles in the nearby Hajar al-Aswad district.

"There is the sound of heavy gunfire. And there is smoke rising from the area. There are already some wounded and residents are trying to flee the area," he said, showing live video images of smoke visible over the skyline. "There are also armoured vehicles heading towards the southern part of the neighbourhood."